UVP EL UVL-28 lamp emission spectra - with and without filter

[JMC]

After a recent post by Andrea on my Katoptaron thread, I've been on the look out for a Blak Ray to give me more UV lighting options. As is often the case there are loads of second hand ones for sale in the US, but not in the UK. However I did find one of their fluorescent tube lamps for sale in the UK on a well known internet auction site.... It was a UVP EL series UVL-28 with 2x 365nm 8w fluorescent tubes. The seller had for some reason got the description wrong though and advertised it as the 254nm version. I was the only one that bid on it and got it for £10.

 

I've done a quick measurement of the emission spectrum of it, with and without the filter in place. Used my OO FX spectrometer, with 600um fiber and cosine corrector, Setup for absolute irradiance measurements. Measured with the end of the cosine corrector 15cm from the tubes. I did 2 scans, one with the filter in place and one with the filter removed. Both were 100ms per scan and 10 scans average. Here's what the look like from 250nm to 850nm.

 

And from 300nm to 450nm.

 

My calibration standard has not arrived for my spectrometer has not arrived yet, so this has yet to be recalibrated for wavelength. However there is a strong line at 405.6nm in my charts which I am presuming is the 404.6nm mercury line. If so then I am about 1nm out in this part of the spectrum which is good to know. The filter does a good job of getting rid of anything above that 404.6nm mercury line, although if you really blow up the y axis, some of the lines from 700nm to 850nm start to become visible even with the filter in place (graph not shown here).

 

The filter itself, I haven't got a transmission spectra for at the moment. My work bench is currently full of other equipment so my light source is packed away. However looking through it at a normal room light, I can see a red glow for the light bulbs, so it looks like it has some transmission at the red end as well as the UV and near UV. The material for the filter is a bit odd, it isn't smooth like a camera lens filter, it has some ripples in it.

 

I'm wondering whether the tubes are interchangeable - it would be quite nice to swap one of the 365nm tubes for a 302nm one and get a broader UV source. I can't use the lamps own filter with that setup, but for UV reflectance imaging that wouldn't be an issue as I'd be filtering on the lens or in the camera. Will have to contact UVP and ask them if there are any issues with using 2 different tubes though before trying it.

 

EDIT - the tubes inside are Hitachi 8W F8T5 Black Light tubes.

[Cadmium]

Sometimes they use Hoya U-325C for UV lights, but if you don't see any violet/blue when you hold it up to a white monitor page, then it is some other U glass.

How thick is the filter, 4mm is standard sheet thickness, and would have the rough surface you describe. What is the overall size?

[JMC]

Steve. I can't get at an edge to measure the thickness, although I have an idea how to measure it. It's in two pieces, each 23.5cm by 2.5cm. It's strange though, when I tap it with my finger nail, it's doesn't sound or feel like glass. Are there any plastic UV filters? I hope to have my light source up and running again this week, so I'll get a transmission spectra through it.

[JMC]

Sometimes they use Hoya U-325C for UV lights, but if you don't see any violet/blue when you hold it up to a white monitor page, then it is some other U glass.

How thick is the filter, 4mm is standard sheet thickness, and would have the rough surface you describe. What is the overall size?

 

Hi Steve, I have got some measurements of the filter. I measured the thickness by putting wooden blocks on eiher side and using my micrometer to measure those. Zeroing it without the filter allowed me to measure the filter thickness. The thickness I got was 3mm. As for the transmission, see below (measured with my OO FX spectrometer), but there was something odd when measuring it which I will explain afterwards;

 

As I was measuring the transmission, I moved the filter around in the beam, and got quite widely varying maximum transmission. The overall curve shape remaining similar, but transmission went up and down in different parts of the filter. The one above was somewhere in the middle of the readings I saw, but max transmission varied between 30% and 80%. I guess there are fluctuations in filter thickness across it, which would account for the ripples I can see. So my 3mm thickness value is, I think, a maximum thickness value.

 

The material is odd too - it doesn't look or feel like glass. Could it be a plastic dual bandpass filter? Is there such a thing?

[JCDowdy]

The filter itself, I haven't got a transmission spectra for at the moment. My work bench is currently full of other equipment so my light source is packed away. However looking through it at a normal room light, I can see a red glow for the light bulbs, so it looks like it has some transmission at the red end as well as the UV and near UV. The material for the filter is a bit odd, it isn't smooth like a camera lens filter, it has some ripples in it.

 

I recall that these used to be a "Woods glass" type filter so you might expect a UG11/5 sort of transmittance. Such industrial grade filters are only intended to filter lamps and so do not need a prohibitively expensive high degree of surface quality.

 

 

I'm wondering whether the tubes are interchangeable - it would be quite nice to swap one of the 365nm tubes for a 302nm one and get a broader UV source. I can't use the lamps own filter with that setup, but for UV reflectance imaging that wouldn't be an issue as I'd be filtering on the lens or in the camera. Will have to contact UVP and ask them if there are any issues with using 2 different tubes though before trying it.

 

EDIT - the tubes inside are Hitachi 8W F8T5 Black Light tubes.

 

They did make a model which had two different lamps, I think a 365nm and a 254nm. On those there is usually a selector switch to operate one or the other. As far as I know these have a simple magnetic ballast and if so most any F8T5 tube should operate in your fixture, with the caveat that the filter may not be appropriate of course. Does your lamp have two filters and are they the same?

[JMC]

They did make a model which had two different lamps, I think a 365nm and a 254nm. On those there is usually a selector switch to operate one or the other. As far as I know these have a simple magnetic ballast and if so most any F8T5 tube should operate in your fixture, with the caveat that the filter may not be appropriate of course. Does your lamp have two filters and are they the same?

 

Hi John. Mine has 2x 365nm tubes, and they both come on at the same time - one switch, turns them both on or off. There are 2 filters, but they are both the same. I spoke with UVP and they said there should be no issue with using one tube of one wavelength and one with another at the same time. So I bought one of their 302nm ones. That turned up today so hope to try it soon. I'd planned on using it without the filter, as that filter would block most of the 302nm tube output.

[ulf]

I measured the spectra from my bug-killing lamp with two unmarked UV-emitting tubes.

These tubes are stronger peak levels in the VIS than Jonathan's quality lamp.

 

 

The lamp might be usable for indoor UV-photography.

Nowadays the sun is at 10° above the horizon at noon. :(

[JCDowdy]

I spoke with UVP and they said there should be no issue with using one tube of one wavelength and one with another at the same time. So I bought one of their 302nm ones. That turned up today so hope to try it soon. I'd planned on using it without the filter, as that filter would block most of the 302nm tube output.

 

Yes, since all F8T5 tubes are made to operate with a standard ballast mixing spectra should work nicely. I have a slightly larger Spectroline XX-15 lamp for which I have a collection of different lamps but I have never needed to mix them. Some of these spectra were published in a paper freely available on PubMed Central

 

Since you have not measured your filter Why don't you try the 302nm tubes with and without the filter to see what you like?

[JMC]

Probably will end up trying it John, just to see.

 

Ok, this is very geeky even for me. I was wondering whether I could see flicker in the tube. So I set the spectrometer to 10 micro-second intervals, and got it to do a full 250nm to 850nm spectrum every 10us for 500 scans. Then I selected a nice strong signal (at 368nm), and plotted the intensity of that signal against the time series scan number from 1 to 50. This is what it showed;

 

The light itself goes on an off on the micro-second scale. It looks to be repeating about every 4 scans or 40us, which works out to about 25kHz. I never knew this before but apparently the ballasts which are used to run fluorescent lights run at 20kHz or higher, so presumably this is the light being switched on and off at very high speed as it is run from the ballast.

 

Good thing I'm not doing any microsecond UV imaging :)

[JMC]

The 302nm tube arrived, and I swapped it in to the lamp, by replacing one of the 365nm tubes. It runs fine. Here are spectra of the 2 tubes individually (OO FX spectrometer set up for absolute irradiance measures, fiber in contact with each tube individually).

 

And spectra from about 20cm away, again setup for absolute irradiance measures. No filter on the lamp - bare tubes.

 

Shame there is such a dip around 340-350nm, but it has a very different characteristic to flash or sunlight, with that big jump in intensity below 320nm. I'm going to try and get some Sparticle shots using the 2x 365nm tubes, and then 1x 302nm and 1x 365nm tube. Not many flowers round here at the moment to try it on unfortunately.

 

The 302nm tube would be an interesting one to try with Invisible Vision's 308nm filter (http://www.invisiblevision.com/products/accessories/).

[Andy Perrin]

Well that looks suitably dangerous, Jonathan! I look forward to the pictures. Wear sunscreen. :-P

[JMC]

Well that looks suitably dangerous, Jonathan! I look forward to the pictures. Wear sunscreen. :-P

Oh yes. I have UV safety glasses and have it pointing away from me at all times when it's switched on.

[dabateman]

Jonathan,

That looks amazing. Very low in the IR region. I didn't even know about 302nm bulbs until you posted this.

Does it get hot?

I have been using two mercury vapour lamps, but they wilt flowers that are sensitive within the time to snap a 300nm shot using my 300bp10 filter. Although I did get one image today, but not much different than 313nm image where I have much more signal.

[JMC]

David, I haven't run it long enough yet to find out how hot it gets. It's only an 8W fluorescent bulb though, so I doubt it gets too hot. One slightly disconcerting thing about it - if you tilt it one way then the other, it sounds like there is something rattling around in it. Manufacturer says apparently that is normal - something to do with the mercury in there.

[JMC]

So I was thinking a 4mm Hoya U-340 filter might be good to try with these tube setups, as it has good transmission between 280nm and 365nm and only about 0.25% transmission at around 710nm. Here is a transmission curve for the U-340 4mm between 250nm and 450nm.

 

This filter should dampen down the contribution above 370nm nicely - the reduced transmission should offset the increased camera sensitivity and stop those longer wavelengths from dominating the image.

 

Using this U-340 filter on a UV Nikkor 105mm with my multispectral EOS 5DSR I took photos of my Sparticle setup with the light about 20cm from the filters. I did this at different exposures, and then white balanced using a PTFE standard illuminated with the UVP light in Darktable. I've chosen images where the brightest image circle was at about max exposure. Firstly the one with the 2 x 365nm tubes (1/4s exposure).

 

And then with 1 x 365nm and 1 x 302nm tube (2s exposure).

 

The image with 2 x 365nm tubes is relatively monochromatic - light spanning a 30nm region from the 355nm, 364nm and 382nm filters. Swapping one of the 365nm tubes for 302nm changes that though - now there is light from 321nm to 396nm, although to be fair there is only a small contribution outside that 355-382nm region.

 

The 2 x 365nm image was at 1/4s exposure and the 1 x 302nm and 1 x 365nm tube was at 2s exposure. On both setups the 365nm light dominates the image though - it is the brightest. Something like 3 x 302nm and 1 x 365nm tube might be a good mix to help emphasize the shorter wavelengths.

 

Be good to have more light in the 340nm region You can get UVA-340 tubes, but only in the 48" length, unless anyone knows of any smaller ones. The 4 foot ones are way to big for me to handle.

 

I'm guessing the emphasis on greens and purples after whitebalancing is because of the spectral distribution of the fluorescence tubes. It is very different sunlight or flash. Be interesting to look at some flowers with it.

 

Oh and David, after the light was on for about 5 minutes, when switched off it was only slightly warm to the touch. It doesn't get very hot. Make sure you have some good safety goggles though.

[JMC]

And just for giggles. Sparticle image using the 302nm and 365nm tube using the same filter, lens, ISO etc, but on the monochrome camera. Except this was at 1/4s (not the 2s for the image above).

 

Much more contribution from the 303nm and 321nm filter now, and much higher sensitivity overall. The 349nm one now reflects the drop in intensity seen in the spectra for the tubes.